Stoker and automatic igniter control system



Sept. 16, 1958 D. T. CAMPBELL 2,851,972

STOKER AND AUTOMATIC IGNITER CONTROL SYSTEM Filed Feb. 1, 1955 2 Sheets-Sheet 1 INVENTOR. DAVID T CAMPBELL.

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A TTORNEK 2 7 1 5 2% m S L 0 R T w L C aw B T M m A m mm om U A D N A R E K o T 5 Sept. 16, 1958 2 Sheets-Sheet 2 Filed Feb. 1, 1955 INVENTOR. DAVID T CAMPBELL BY A 770 RNEY United States Patent STO ER AND AUTOMATIC IGNITER CONTROL SYSTEM David T. Campbell, Indianapolis, Ind. Application February 1, 1955, Serial No. 485,387

1 Claim. (Cl. 110-1 This invention relates to stoker-fed, solid-fuel burners and is concerned primarilywith the provision of an automatic ignition system for such burners.

It is the primary object of this invention to provide a dependable and relatively simple means for and method of igniting the fuel in a stoker-fed, solid-fuel burner when no combustion exists in the burner.

A principal object is to provide a method ofand means for automatically igniting the fuel in a stoker-fed, solidfuel burner when no combustion exists in the burner.

Another principalobjectof this invention is to provide a method of and means foractivating an igniting unit and actuating a stoking unit for a solid-fue1 burner in timed relation so as to attain safe, economical operation and the optimum efficiency balance between time economy and dependability of ignition;

Another important object of the invention is to provide a method of and means foractivating an igniting unit and actuating a stoking uni-tof a solid-fuel burner according to a cycle wherebythe stoker is first put into operation, the ignitervunit is subsequently activated, then the stoker continues to operate, stops; and commences to operate again following successive, significant time intervals, and the igniter unit is thereafter deactivated-while the stoker unit continues to. operate.

Further objects of the invention will appear as the description proceeds.

To the accomplishment of the above and related objects, my inventionmay be embodied in the form illustrated in the accompanying drawings and in the steps hereinafter described, attention being called to-the fact, however, that the drawings are illustrative only, and that change may be made in the specific construction illustrated and described, and in the procedure. recited, so long as'the scope of the appended claim is not violated.

Fig. 1 is a perspective view, more or less diagrammatic, showing the type of burner and stoker arrangement with which my inventionis particularly adaptable;

Fig. 2 is a sectional view, more or less diagrammatic, through the firepot of the burner of Fig. 1, illustrating an optimum arrangement of an igniter unit therein;

Fig. 3 is a perspective view of such an igniter unit; and

Fig; 4 is a schematic wiring diagram of the electrical components-constituting a part of my invention, showing the cycle control unit at rest.

Referring more particularly to. the drawings, I have shown in Fig. 1;, somewhat,diagrammatically, a solid-fuel burner and stoker arrangement with which my invention is particularly adaptable. Such arrangement is fully illustrated and described in my Patent No. 2,600,614, issued June17, 1952.,

A burner. (shown in phantom outline) defines a combustion chamber in which is located a tuyered firepot 11. Surrounding the firepot 11, communicating with the tuyeres. thereof, and extending outside the burner 10 is a duct or wind box 12. A fuel delivery conveyor in the formofv a, tube 13, having arranged therein a conveyor screw 14, passes through the duct 12 to communicate with the firepot 11, the other end thereof receiving fuel from a fuel reservoir 15 in accordance, for instance, with the disclosure of my above-mentioned Patent No. 2,600,614. Drive means, illustrated generally by the reference numeral 16, is connected to rotate screw 14 (see Fig. 2) within said tube to feed fuel to the firepot under controlled conditions. A blower 17, driven by drive means 16, delivers air through a conduit 18 to duct 12 and thence into the burner combustion chamber.

In similar systems, it is conventional practice to maintain the firepot and the proximal portion of the delivery tube tightly packed with fuel to prevent smoke from passing back through the tube. However, in the arrangement of my Patent No. 2,600,614, I have deliberately eliminated this feature and, instead, have maintained the fuel in a shallow layer in the tube and only loosely packed in the throat of the firepot.

For the purposes of this invention, it is necessary, if not essential, that the delivery tube merge with the firepot in a smooth curve, as at 20. I have found that by driving screw 14 according to the teachings of Patent No. 2,600,614, and by extending the screw into the curved portion 20, the fuel will be relatively tightly packed about the outer wall 21 of portion 20 but only loosely packed along the inner wall 22 of the curved portion 20 as indicated in Fig. 2.

The conventional firepot 11 is formed with double walls 23 and 24, annular in shape, the inner wall 23 thereof having a plurality of induction ports 25 about the upper portion thereof communicating with the region between the two walls. The duct 12 also communicates with such region through suitable ports 26. Combustion supporting air is forced through ports 25 into firepot 11 and so into the combustion chamber. The primary combustion of the fuel takes place, therefore, immediately adjacent these ports 25, and it has been found that there is a definite plane 27, between the burning fuel and the raw fuel, including the lower extent of ports 25.

Beneath this plane 27 and on the inside wall 22 'of the curved throat 20, I locate my igniter unit 28. So placed, the unit is out of the combustion zone of the firepot and in that region where the fuel is the most loosely packed. Therefore, by locating a by-pass scoop 19 in the blower 17, as disclosed in my Patent No. 2,600,614, and directing a part of the air from blower 17 into tube 13, a combustion supporting draft can be maintained past the igniter unit 28. This is only possible where the fuel is maintained in loosely packed condition in throat 20 and is not possible in the conventional burner because of the reasons stated above in regard to preventing smokeback through tube 13.

The igniter unit 28 is preferably in the form of a U with the curved end 29 thereof bent out of the plane of the legs 30 and 31. Only that portion 29 is placed within the firepot, and, as can be seen from an inspection of the drawings, presents a relatively small heating surface to the fuel within the firepot.

Preferably, a lip 32 is integrally formed in the wall 22 to deflect the flowing fuel away from direct frictional contact with the igniter unit.

Only a few bits of coal will bear directly against the igniter unit at any time. In spite of the small heating surface presented by the igniter unit, it has been found that a unit of 300 watts is sufficient to raise these few pieces of fuel in contact therewith, to their kindling temperature in about four miutes. Because of the loosely packed condition of the fuel in the immediate vicinity of the unit 28, sufficient air may be forced through the fuel bed to cause the heated bits of fuel to ignite and the ignition of only these bits is suificient then to ignite the entire fuel bed within a very few minutes.

Drive means 16 includes a motor 33 and since this motor drives both the fuel feeding means and theblower, it will hereinafter be referred to as the stoker motor.

The electrical control system for the igniter and stoking units comprises an on-off switch unit 34, room thermostat 35, cycle control unit 36, and stack thermo-responsive control unit 37. A hold fire control unit 38 may also be provided, the details and function of which will be set forth later in this description.

Cycle control unit 36 is shown at rest in Fig. 4 and includes three switches 39, 4t) and 41 which are opened and closed by cams 42, 43 and 44, respectively. Cams 42, 43 and 44 are mounted on a common shaft 45. Shaft 45 is driven by the cycle motor 46 which is connected to drive shaft 45 through one revolution in twenty minutes. Terminals 4'7, 48, 49, 50 and 51 provide convenient points of connection when installing the electrical control system.

Stack thermo -responsive control unit 37 effects its control of function automatically in response to temperature changes at the smoke pipe or stack 93, and for the specific details of this unit reference is made to my copending application Serial No. 376,641, filed August 26, 1953. Essentially, this unit includes a bimetallic bar 52 which is responsive to temperature changes at the stack 93 upon which the stack thermo-responsive control unit 37 is mounted. Also included in this unit are single pole limit switch 53 and double pole switch 54, both of which are actuated by movement of the thermo-responsive bimetallic bar 52. Limit switch 53 opens when the stack reaches a temperature of 650 F. Movable contact 55 of switch 54 is in engagement with fixed contact 57 when the stack temperature is below 115 F. and in engagement with fixed contact 56 when the stack temperature is above this value.

Terminals 58', 59, 68' and 60A provide convenient points for connecting wire leads to this unit.

The electrical control system operates as follows. Up-

on a call for heat from the room thermostat (at a time when no combustion exists in the burner), each of switches 39, 4t) and 41 will be open, switch 53 will be closed and movable contact 55 of switch 54 will be in engagement with fixed contact 57. A closed circuit will thereby be established from one side of a conventional household electrical power source (not shown) through line 58, switch 59, line 60, thermostat 35, line 61, line 62, switch 53, line 63, line 64, contacts 55 and 57 of switch 54, line 65, line 66, line 67, cycle motor 46, line 68, line 69 and thence to ground 99 or the other side of the power source through line 91.

After the cycle motor runs for thirty seconds, driving shaft 45 in a clockwise direction, cam 44 closes switch 41 to provide a closed circuit from line 61 (which leads eventually to one side of the power source), through line 62, switch 53, line 63, line 64, switch 54, line,65, line 66, line 74 switch 41, line 71, line 72, stoker motor 33, line 73, line 74, line 69, and thence to ground 90 or the other side of the power source. By this circuit, stoker motor 33 is actuated and fresh fuel is fed past the igniting unit 28.

Twenty seconds after the stoker motor starts, cam 42 closes switch 39 to provide a closed circuit from line 61 (which leads eventually to one side of the power source), through line 62, switch 53, line 63, line 77, line 76, switch 39, line 75, line 67, cycle motor 46, line 68, line 69 and thence to the ground side of the power source. Due to the configuration of cam 42, switch 39 remains closed during the rest of the cycle and this insures that the full cycle will be completed even though the stack rises to a temperature of over 115 F. at an intermediate period during the cycle.

Ninety seconds after the start of the cycle and sixty seconds after the stoker motor 33 is actuated, cam 43 closes switch 40 to provide a closed circuit from line 61 (which leads eventually to one side of the power source) through line 62, switch 53, line 63, line 64, switch 54, line 65, line 66, line 75, line 78, switch 40, line 79, line 80, igniting unit 28, line 81, line 74, line 69 and thence to the ground side of the power source. By this closed circuit, the igniting unit 28 is activated.

Three minutes. after the start of the cycle and while the igniting unit remains activated, cam 44 opens switch 41 and stoker motor 33 is thereby deenerized. Due to the configuration of cam 44, the stoker motor remains quiescent for a period of three and one-half minutes during which time the igniting unit heats the newly fed fuel above the kindling temperature. At the end of this three and one-half minute period, cam 44 again closes switch 41 and stoker motor 33 is again actuated.

Seven minutes after the start of the cycle and onehalf minute after the stoker motor is again actuated, cam 43 opens switch 40 and the igniting unit is thereby deactivated. Since the igniting unit is located below the normal level of combustion in the burner, and since the stoker continues to feed fuel past the igniting unit after the igniting unit is de-activated, the ignited fuel will be moved away from the igniting unit very promptly after ignition, and the useful life of this unit will thereby be significantly prolonged.

The stoker motor and cycle motor continue to operate for thirteen minutes after the igniting unit is de-activated. At the end of this time, switches 39 and 41 will be opened by cams 42 and 44, respectively, and the cycle motor will be at rest position shown in Fig. 4. 7

Provided the fuel in the burner is successfully ignited (as will normally be the case), the temperature of the stack will have exceeded 115 F. and movable contact 55 of switch 54 will have moved out of engagement with fixed contact 57 into engagement with fixed contact 56. This establishes a closed circuit from line 60 (which leads eventually to one side of the power source), through thermostat 35, line 61, line 62, through switch 53, line 63, line 64, switch 54, line 82, line 83, line 72, stoker motor 33, line 73, line 74, line 69 and thence to the ground side of the power source. By this circuit, actuation ofthe stoker motor will be subsequently governed by the demands of room thermostat 35 for so long as contact 55 is held in engagement with contact 56.

If, due to abnormal conditions, the fuel is not successfully ignited during the first cycle, movable contact 55 of switch 54 will not have moved out of engagement with fixed contact 57 and the cycle will repeat itself until ignition is successfully effected.

If, at any time, the stack temperature should exceed.

650 F., limit switch 53 will open and the stoking unit will be de-actuated regardless of any demand by the room thermostat. Switch 53 therefore operates as a safety means to prevent overheating.

It is noted that so long as combustion exists, the cycle control unit does not operate and has no part in the stoker operation. That is, so long as the fuel is burning, movable contact 55 of switch 54 will be in engagement with fixed contact 56, and switches 39, 40 and 41 of the cycle control unit will be by-passed.

A hold-fire control unit 38, mentioned earlier, is shown in ghost lines in Fig. 4 and may be provided for use under emergency conditions or when a high percentage of fines in coal causes ignition failure. This hold-fire control unit operates on a predetermined time cycle without regard for the demands of the room thermostat.

The hold-fire control unit includes motor 84 which actuates a cam (not shown) which in turn opens and closes switch 85 according to the predetermined time cycle.

To render the hold-fire control unit effective, several changes in the wiring scheme shown in Fig. 4 are necessary. First, lines 86 and 87 are connected between the power source and motor 84. Motor 84 therefore will run continuously. Line 89 connects switch 85 to line 61. Line 66 is disconnected from terminal 49. Line 77 is disconnected from terminal 50 and connected to terminal 47. Upon closing of switch 85 by a cam driven by motor 84, a closed circuit will be established from one side of the power source through line 58, switch 59, line 87, line 88, switch 85, line 89, line 61, line 62, switch 53, line 63, line 77, terminal 47, line 72, stoker motor 33, line 73, line 74, line 69 and thence to the ground side of the power source. The stoking unit will run intermittently thereafter as determined by the predetermined opening and closing of switch 85 without regard for the demands of the room thermostat.

If the stack temperature should exceed 650 F., limit switch 53 will open as previously described, and the stoking unit will be de-actuated regardless of closure of switch 85.

I claim as my invention:

In combination with a solid-fuel burner comprising a combustion chamber, a fuel conveyor tube connecting said chamber with a source of fuel, screw means arranged in said tube to convey fuel between said fuel source and said chamber, an electrically-energizable igniter unit arranged in, and exposed to fuel within, said tube, draftproducing means for forcing air past said igniter unit into said chamber, a first electric motor connected to drive said screw means and said draft-producing means, and electrical control means for controlling said igniter unit and said electric motor comprising a second electric motor, a room thermostat, a normally-closed switch responsive to temperature conditions in said combustion chamber to open at temperatures above a predetermined value, a double pole switch responsive to temperature conditions in said combustion chamber to occupy a first position in the absence of combustion in said chamber and a second position in the presence of combustion therein, a first energizing circuit for said second motor completed through said room thermostat, said normally-closed switch, and said double pole switch when in its first position, a first normally-open switch, a second normally-open switch, a third normally-open switch, cam means for each of said normally-open switches driven by said second electric motor, a first energizing circuit for said first motor completed through said room thermostat, said normallyclosed switch, said double pole switch when in its first position, and said first normally-open switch, a second energizing circuit for said second motor completed through said room thermostat, said normally-closed switch, and said second normally-open switch, an energizing circuit for said igniter unit completed through said room thermostat, said normally-closed switch, said double pole switch when in its first position, and said third normally-open switch, said cam means for said first normally-open switch acting to close the same promptly after energization of said second motor, to hold the same closed for a predetermined period, then to open said switch for a further period and then to close said switch for the remainder of a cycle, the cam means for said second normally-open switch acting to close the same promptly after initial closing of said first normally-open switch and to hold said second normally-open switch closed throughout the remainder of such cycle, and the cam means for said third normally-open switch acting to close the same shortly before reopening of said first normally-open switch, to hold said third normally-open switch closed throughout the said further period during which said first normallyopen switch remains open, and to reopen said third normally-open switch shortly after said first normally-open switch is reclosed, and a' second energizing circuit for said first motor completed through said room thermostat, said normally-closed switch, and said double pole switch when in its second position.

References Cited in the file of this patent UNITED STATES PATENTS 1,844,026 Banfield Feb. 9, 1932 2,100,284 Kreichbaum Nov. 23, 1937 2,210,720 Johnson Aug. 6, 1940 2,385,811 Hotchkiss Oct. 2, 1945' 

